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Formula: Pb2(OH)2[(UO2)(CO3)2]
Anhydrous carbonate, uranyl mineral
Crystal System: Orthorhombic
Specific gravity: 6.89 calculated
Hardness: 2
Streak: Pale yellow
Colour: Yellow, very pale greenish yellow, colourless
Luminescence ; Not fluorescent under UV
Solubility: Soluble in dilute nitric acid with evolution of carbon dioxide
RADIOACTIVE
Environments
Localities
At the Jánská vein, Březové Hory deposit, Březové Hory, Příbram, Příbram District, Central Bohemian Region, Czech Republic, the
rare uranyl lead carbonate widenmannite was
found where two generations occur in several morphological types and mineral associations in hydrothermal veins; these two
generations have different ages, and both have a dominance of non-radiogenic Pb which originates from weathered
galena. The older widenmannite I forms fine-grained, grey to beige aggregates in the
highly altered supergene part of the hydrothermal ore vein, in
association with pyromorphite, cerussite
and goethite. The younger widenmannite II occurs as white, yellow or
greenish-yellow thin tabular crystals up to 0.5 mm long in association with cerussite,
anglesite, limonite,
kasolite and an unnamed lead -
uranium - oxygen phase. It is suggested that widenmannite decomposes in several
steps, with lead uranate PbUO4 as the final product
(MM 74.1.97–110).
Widenmannite from the Jánská vein - Image
At the type locality, the Michael Mine, Weiler, Seelbach, Seelbach, Ortenaukreis, Freiburg Region, Baden-Württemberg, Germany,
widenmannite occurs as a rare secondary mineral in the oxidised zone
of a hydrothermal arsenic– lead- bearing deposit,
associated with hügelite and hallimondite,
as fragile tabular yellow crystals in radiating bundles in cavities in chert and with
cerussite on altered galena
(AM 47.415, HOM).
Widenmannite from the Michael Mine - Image
At the Loe Warren Zawn, Botallack, St Just, Cornwall, England, UK, widenmannite, an extremely rare mineral, occurs in a
localised patch of lead - uranium -
copper mineralisation exposed near the base of the cliff, well above high-tide level, at
the back of a narrow cove (locally known as a 'zawn').
A line of sporadic uraninite mineralisation with associated
supergene products can be traced across the back of Loe Warren zawn. At one
end, this line intersects an area containing swarms of veinlets carrying chalcocite
with minor chalcopyrite and pyrite. Surface
water draining from rubble at the base of the cliff trickles continuously over this mineralised area and has led to the formation
of a rich assemblage of supergene carbonates and phosphates.
Widenmannite occurs as transparent, colourless to very pale greenish yellow, lath-like crystals. Most commonly the laths
form mats encrusting the matrix, or are arranged in stellate groups; rarely they form free-standing loose spheroidal aggregates;
white, anhedral flaky masses are also common. The laths are rarely more than 10 microns wide, but may reach 100 microns in length.
Radiated groups and tufts of bright yellow doubly-terminated tapering crystals of
dewindtite are associated with widenmannite on a number of specimens. Other
associated minerals include
torbernite-zeunerite,
kasolite, cerussite,
malachite, amorphous copper silicate and rarely
cumengeite. Botallackite,
atacamite, connellite and
lavendulan occur sporadically in the same area.
Widenmannite was also noted in a small patch of supergene alteration
of uraninite about 3 m NE of the main exposure. This area is relatively dry and the
widenmannite occurred as white flaky masses on a biotite-rich matrix with
kasolite and arsenic-rich
torbernite.
Widenmannite and dewindtite appear to be the last-formed
uranium species at Loe Warren zawn, with the chlorides
cumengeite, connellite and
botallackite formed last of all, presumably by the action of sea spray on
pre-existing lead and copper species
(MM 59.4.745-749).
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